Geomechanics and Ground Control · Geomechanics · 2 marks · Multiple choice
A 50 mm diameter rock sample fails under 120 kN uniaxial compression on a plane inclined 60° to the horizontal as shown. Find normal and shear stresses on that plane, respectively, in MPa.
Axial compressive stress is 120000/(π×50²/4)=61.1155 MPa. The failure plane is 60° from the horizontal principal plane, so σn=σ cos²60°=15.2789 MPa and τ=σ sin 60°cos 60°=26.4638 MPa. Hence A. The sample’s full circular area gives axial stress; resolve that stress onto the inclined plane.
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